Hydraulic flow difference sensor and shutoff apparatus

ABSTRACT

A shutoff valve mechanism is placed in a hydraulic system line extending between a source of hydraulic fluid under pressure and a utilizing apparatus such as a subsystem or a hydraulic actuator. Variable orifices disposed in the source and return flow paths produce pressure drops which vary linearly proportional with flow rate. The pressure drops are compared and in the event of a predetermined difference therebetween, the shutoff valve is actuated to isolate system pressure.

United States Patent [191 Wiggins Nov. 13, 1973 HYDRAULIC FLOWDIFFERENCE SENSOR AND SHUTOFF APPARATUS [75] Inventor:

[73] Assignee: Textron Inc., Providence, R1.

[22] Filed: May 22, 1972 211 Appl. No.: 255,743

Don A. Wiggins, Saugus, Calif.

[52] U.S. C1. 137/100, 137/625.62 [51] Int. Cl. G05d 11/02 .[58] Fieldof Search 137/87, 100, 498,

[56] References Cited UNITED STATES PATENTS 1,558,529 10/1925 Wunsch137/100 2,493,906 1/1950 3,233,623 2/1966 3,408,865 11/1968 Chenault73/208 3,502,102 3/1970 Maltby 137/498 5 FOREIGN PATENTS OR APPLICATIONS1,807,335 7/1969 Germany l37/625.62

Primary Examiner-William R. Cline Attorney-Billy A. Robbins et al.

[57] ABSTRACT 7 Claims, Drawing Figures Zigzag 2% FLOW RATE SEA/5oz LLIOFF 2 FEESSUREWSA (\svsrem SUPPLV) VALVE k K r (/0 /4 4 /8 60B swore/v!(UT/L/Z/A/G nPPAeATus) /2s //2 //8 J l 24 34 2 50 28 26 svsrem lCl-IECKl L J/-2ow RATE SEA/SO21 I EETUQN' mLl/E [*fifivsrem RETURN) BACKGROUNDOF THE INVENTION It has long been desirable to provide apparatus wherebya loss of hydraulic fluid can be prevented in the event a rupture orleak occurs in a branch circuit which is included as part of the overallsystem. If such leakage cannot be precluded, then substantially theentire source of hydraulic fluid is dissipated through the rupture orleak, thus rendering the entire hydraulic system inoperable to theultimate malfunction of the apparatus in which the system is included.Prior art apparatus to accomplish the foregoing has included fuse-typehydraulic shutoff valves which are operable only in the event the flowrate of hydraulic fluid exceeds a certain predetermined design value.With such devices, it was found that in the event a relatively smallleak occurs not permitting the designed flow rate indicative of failure,the leak was undetected with the ultimate result of system failure. Inaddition, such fuse-type valves are usually incapable of detectingtransient flow surges as distinguished from a rupture in the branch lineand tend, therefore, to shut off the flow to the utilizing apparatus inthe event of such a transient surge.

To overcome the foregoing disadvantages, flowoperated shutoff valveshave been constructed which effectively compare the rate of fiow in thesource and return flow paths leading to and from the utilizing apparatusand develop through flow control orifices a pressure drop which isapplied directly to a piston so that resultant forces are compared whichtend to move a control spool into such a position as to shut off theflow of fluid from the source. Although such apparatus operate extremelywell in the event of a major rupture, it has been found that when arelatively small difference exists between the source and return flowrates, the apparatus is not capable of actuating the shutoff valve inresponse to such differences.

FIELD OF THE INVENTION This invention relates to hydraulic systems suchas A employed on vehicles, aircraft, ships and the like, and

more specifically to sensing, controlling and maintaining the flow ofvital fluid. More specifically, the invention relates to a shutoffapparatus responsive to flow rate difference between two critical pointsin a fluid stream which will sense leaks occurring between such pointsand isolate the same.

SUMMARY OF THE INVENTION First and second means for producing first andsecond pressure drops which vary linearly proportional to flow rates infirst and second critical flow paths respectively. Means for comparingthe first and second pressure drops and providing an output signal inresponse to a predetermined magnitude of difference therebetween. Meansresponsive to the output signal for shutting off fluid flow.

shutoff valve which has not heretofore been possible. Such apparatus iscapable of operating in the event of a steady state operationalcondition wherein no fluid flow demand is being placed upon the systemby the utilizing apparatus other than that required to accommodatenormal leakage. On the other hand, it is capable of operating in theevent of major demands by the utilizing apparatus upon the system. Ineither event, the apparatus can detect relatively minute flow ratedifferences, amplify the same, and utilize the amplifier signal toeffect shutoff of fluid flow in the event of predetermined discrepancybetween the flow rates.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationpartlyin block form illustrating apparatus constructed in accordancewith the present invention;

FIG. 2 is a cross-sectional drawing of the source fiow path and shutoffvalve of apparatus constructed in accordance with the present invention;

FIG. 3 is a cross-sectional illustration of a return flow path ofapparatus constructed in accordance with the present invention;

FIG. 4 is a schematic representation of the variable orifice definingportion of the apparatus constructed in accordance with the presentinvention; and

FIG. 5 is a graph illustrating the variation of pressure drop versusflow rate utilizing apparatus constructed in accordance with the presentinvention.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Referring now to FIG. 1,there is schematically illustrated a shutoff apparatus which is actuatedby sensing the difference in flow between first and second fluid flowpaths constructed in accordance with the present invention. As istherein shown, a source of fluid under pressure (P,) 10 is connected bya conduit 12 to a flow rate sensor 14. As is indicated by theparenthetical description (system supply) the flow rate sensor 14 isconnected in the first fluid flow path which is connected to the sourceof fluid under pressure or system supply. The flow rate sensor, as willbe described more fully hereinafter, produces a pressure dropthereacross which is linearly proportional to flow rate therethrough.The flow rate sensor 14 is connected by a conduit 16 to a shutoff valve18 which is normally open. A conduit 20 interconnects a subsystem(utilizlng apparatus) 22 to the shutoff valve 18 while an additionalconduit 24 connects the subsystem to a flow rate sensor 26 which is inthe (system return) fluid flow path. As is indicated by illustrating theconduits 20 and 24 as broken, the utilizing apparatus or substystem 22may be disposed at any position desired remote from the remainder of theapparatus illustrated in FIG. 1.

A conduit 28 connects the flow rate sensor 26 to a check valve 30 whichin turn is connected by a conduit 32 to system retum- 34 which is thereturn for the source of fluid under pressure (P,) 10. System sourcefluid pressure, which exists on the upstream side of the flow ratesensor 14, is conducted through a conduit 36 and conduit 38 to a firstchamber 40 positioned within a differential pressure detector 42. Aconduit 44 which is interconnected to the conduit 16 conducts the fluidpressure on the downstream side of the flow rate sensor 14 to a secondchamber 46 within the differential pressure detector 42. The chambers 40and 46 are separated by a pressure-sensing flexure means such as thebellows 48. As is'well known in the prior art, the bellows 48 willexpand or contract depending upon the differences in the fluid pressureappearing in the chambers 40 and 46. Since such systems are well knownto the prior art, no further illustration or description thereof will begiven herein.

A conduit 50 interconnects the system return fluid pressure, whichexists on the upstream side of the flow rate sensor 26, to a firstchamber 52 of a second differential pressure detector 54. A conduit 56interconnects the pressure in existence on the downstream side of theflow rate sensor 26 to a second chamber 58 in the differential pressuredetector 54. The chambers 52 and 58 are separated by a secondpressure-sensing flexure means such as a second bellows 60 whichoperates in the manner as described with respect to bellows 48hereinabove.

A connecting rod 62 is rigidly affixed to the bellows 60 and 48 andmoves as the bellows 48 and 60 expand and contract responsive to thepresence of differential pressures in their respective chambers. Aflapper 64 is pivotally connected at the point 66 to the connecting rod62. The flapper 64 is pivotally suspended at the pivot point 68 androtates thereabout. The end 70 of the flapper 64 is suspended betweenthe outlet orifices of a pair of nozzles 72 and 74. Each of the nozzles72 and 74 is connected through a restriction orifice 76 and 78respectively and a filter 80 and 82 respectively to system sourcepressure P, as is illustrated. The chamber 84 within which the nozzlesand the flapper are disposed is connected by way of the conduit 86 andthe conduit 56 to the conduit 32 which is connected to system return 34.

The nozzle 72 is connected through the conduit 88 to a chamber 90 whilethe conduit 92 connects the nozzle 74 to a chamber 94. The chambers 90and 94 are formed by a way of a cylinder 96. Disposed also within thecylinder 96 is a valve in the form of a spool 98. The spool 98 includeslands 100-102 which are interconnected by a reduced diameter portion104. A reduced diameter extension 106 from the land 100 abuts a piston108 which is also disposed within the cylinder 96 and rests against astop member 110. A spring 112 is disposed within the chamber 94 againstone end of the cylinder 96 and abuts the land 102 thereby constantlyurging the spool 98 toward the left so that the piston 108 is in contactwith the stop 110.

Damper means 114 is also disposed in the chamber 94 and includes thecylinder 116 within which there is disposed a plunger 118 which isconnected at one end to the land 102. Disposed internally of the plunger118 is a flow path 120 having a restriction means 122 at the mouththereof. The damper means prevents inadvertent operation of theapparatus during transients in the system. Such a damper apparatus isrequired as a result of the extremely quick response of the detectionportion of the system in addition to the compressibility of hydraulicfluid and inherent lag times in the system. Such considerations causesupply and return flow to not be exactly equal, even though a leak doesnot in fact exist, during the initial part of the transient command.

A conduit 124 is interconnected by way of the conduits 36 and 12 to thesystem source of fluid under pressure 10 and to a port 126 in thecylinder 96. A port 128 in the cylinder 96 is connected by a conduit 130to the shutoff valve 18 as will be described more fully hereinafter. Anadditional conduit 132 connects system return, by way of the chamber 84,to the space 134 within the cylinder 96 between the lands 100 and 102.As a result, under normal operating conditions, that is, when no flowdifference is detected, system return is connected through the space 134to the shutoff valve 18 maintaining the same in a normally opencondition. It should be noted that the land 100 closes the port 126under these conditions. In addition thereto, a conduit 136 is providedthrough the land 100 interconnecting the spaces 134 and 138 within thecylinder 96, space 138 being defined between the land 100 and the piston108.

In operation of an apparatus as schematically illustrated in FIG. 1, abreak in the conduits 20 or 24 or a malfunction in the subsystem 22causing leakage of the hydraulic fluid is detected and the shutoff valveis actuated. As an example, assume that a break has occurred in the line24 thus causing hydraulic fluid to be lost therethrough. Such break inthe line 24 creates an additional demand upon the source of fluid underpressure 10 resulting in an increased flow rate of hydraulic fluid. Suchincreased flow rate of fluid causes an increased drop in pressure acrossthe flow rate sensor 14. Therefore, the pressure appearing in thechamber 40 is increased with respect to the pressure appearing in thechamber 46 of the differential pressure detector 42. Since a break hasoccurred in the conduit 24, there will be a reduced flow rate throughthe system return flow path and the flow rate sensor 26. As a resultthereof, the overall pressure drop created by the flow rate sensor 26 isless than that which has been created by the flow rate sensor 14. Thus,there will be a reduced pressure differential appearing across thebellows 60.

As a result of the differences in differential pressure, the forcecreated by the increased pressure in the chamber 40 causes the rod 62 tomove toward the right as viewed in FIG. 1 rotating the flapper 64clockwise. The end of the flapper therefore is positioned closer to theorifice of the nozzle 72. As is well known in the prior art, thepressure appearing in the conduit 88 and in the chamber increases as aresult of such positioning of the end 70 of the flapper 64 while thepressure appearing in the conduit 92 and the chamber 94 decreases. As aresult thereof, the force generated as a result of the increase inpressure in the chamber 90 acting against the outer surface of thepiston 108 moves the spool 98 toward the right against the force of thespring 1 12 and the damper 114. As the spool 98 moves toward the right,the opening into the cylinder 96 by way of the conduit 132 is firstclosed by the land and then the port 126 is opened, thus removing returnfrom the space 134 and connecting the system pressure to the space 138.System pressure appearing in space 138 immediately propels the spool 98toward the right to its limit of travel and interconnects systempressure through the space 138, the conduit 136, the space 134, and theconduit to the shutoff valve 18. The shutoff valve 18 then actuatesthereby closing the interconnection between the conduits l6 and 20 thusdepriving the conduits 20 and 24 and the subsystem 22 of the source offluid under pressure and isolating the leak. The presence of sourcepressure in space 138 also locks the spool to the right as viewed inFIG. 1 thereby also locking the shutoff valve in its actuated positionso long as source pressure is applied. Upon release of source pressure,the spool and the shutoff valve return to their respective non-actuatedpositions.

It will immediately be noted by those skilled in the art that in theevent the flapper end 70 moves closer to the nozzle 74, nothing willoccur since the pressure in chamber 94 increases with respect to that inchamber 90 and the entire apparatus is already against the stop 110.However, it will also be recognized that this condition cannot occurunder operating circumstances of apparatus in accordance with thepresent invention. The nozzle 74 and the accompanying interconnectionswith respect thereto are utilized to render the system, insofar as theflapper nozzle portion thereof is concerned, insensitive to returnpressure variations as normally occur in typical hydraulic systems.

Referring now more specifically to FIG. 2, there is illustrated in across-sectional view the flow rate sensor 14 and shutoff valve 18. As isshown, there is provided a housing 150 which defines the bore 152.Positioned within the bore is a cylinder 154 which is spaced inwardlyfrom the surface of the bore 152 to provide a flow path 156 surroundingthe cylinder 154. The cylinder 154 is positioned against a shoulder 158provided in the bore and is sealed by an O-ring 160 as is well known inthe art. A hollow piston 162 is slidably disposed within the cylinder154 and is spring-loaded by a spring 164 so as to be urged constantlytoward the left as viewed in FIG. 2. A stop means in the form of awasher 166 having flow ports 168 defined therein is held in placeagainst the outer surface 170 of the cylinder 164 by the fitting 172through which there is provided communicating openings 174.

A plurality of openings 176, 178, 180 and 182 are provided in the wallof the cylinder 154. When the piston 162 is in the position illustratedin FIG. 2, the plurality of openings 176-182 are closed.

In operation as the fluid under pressure enters through the conduit 12and into the bore 152 of the housing 150, the fluid pressure thereof istransmitted through the opening 168 and the conduit 36 to the pressuredifferentialy detecting member 42 as above described. At the same time,the flow of fluid operates against the surface 184 of the piston 162 tomove it toward the right against the force of the spring 164. As thepiston 162 moves toward the right, the openings 176 and 180 in thesurface of the cylinder 154 are gradually opened. The amount of theopening depends upon the amount of force created by the fluid underpressure acting against the piston 162. As the various openings arefurther opened by the movement of the piston 162, a flow path is createdthrough the conduit 12, the openings 176-182 and the chamber 156 throughthe conduit 20 as above described.

The construction of the flow rate sensor 26 in the system return flowpath is illustrated in detail in FIG. 3 and is identical to thatillustrated in FIG. 2 and immediately above described. Therefore thevarious parts thereof are designated by utilizing the same referencenumerals primed as are used in FIG. 2. Thus, it will be recognized thatthe flow rate sensor and system return is disposed within a bore 192defined by the housing 190 in such a manner that a flow path 194 isdescribed about the outer surface thereof and through the plurality ofopenings 176-182 provided in the cylinder 154' thereof.

In accordance with one of the features of the present invention, it isrecognized that to permit an accurate comparison of the flow from thesource and to the return, a linear relationship between the differentialpressure across the orifice of the flow rate sensor with respect to theflow rate is required. Such a linear relationship allows theestablishment of a predetermined difference in the flow rate to thereturn as compared to the flow rate from the source as the threshold, orminimum, to effect actuation of the shutoff valve. Thus, whether theabsolute flow rate be small or large, with the linear relationship, thesame differential pressure is produced and the apparatus may be adjustedto respond thereto. In the prior art, where fixed orifices, or orificeswith improper sizing, were used, the relationship between flow rate anddifferential pressure followed a relationship where differentialpressure varied proportionally to the square of the flow rate. Thus, forhigh flow rates in the system, a small difference in source and returnflow rate created a large difference in pressure drops across theorifices. However, where very low flow rates were in existence, asduring normal steady state operation, a very small difference inpressure drops across the orifices is produced by the same difference inflow rates. Therefore, a different sensing mechanism is needed to detecta leak at low flow rates from that operable at high flow rates. If theprior art system uses the low flow rate differential pressure as thethreshold, then the system becomes too sensitive and shuts downspuriously from normal system pressure variations. To provide such alinear relationship, it can be seen from the basic orifice flow equationthat it is necessary to permit the flow area of the orifice. to changeproportionally to the square root of the pressure drop across theorifice. The basic orifice flow equation is: i

Q Const. X A X (D,,)

Where:

Q flow Const. constant A the area of the orifice D, the pressure dropacross the orifice In accordance with the foregoing, the plurality ofopenings or flow orifices 176482 in each of the flow rate sensors isconstructed as is illustrated generally in FIG. 4 to which reference ishereby made. As is therein illustrated, the areas of flow orifices 176and are contoured to increase as the piston 162 moves toward the rightas viewed in FIG. 4. However, from the flow equation, the area of theflow orifices increases inversely proportional to the square root of thepressure drop across the orifice.

As will also be recognized, the orifices 178 and 182 are larger in sizethan orifices 176 and 180. When the utilizing apparatus 22 is in atransient condition of operation, such, for example, as when a commandhas been given to a hydraulic actuator to move from one position toanother, there is a temporary but large demand for flow of hydraulicfluid from the source thereof to the utilizing apparatus. Under theseflow conditions, the piston 162 is caused to move more drastically thanunder conditions of steady state operation, that is, when the actuatoris merely being maintained in its static condition. As a result, thefiow rate sensor must be capable of detecting such differences and stillmaintaining the capability of comparing the system supply flow rate withsystem return flow rate to and from the subsystem and detectingdifferences therebetween as would be in existence in the event of arupture or other leak in the system. In so doing, however, the increasein area of the flow orifices 178 and 182, which are utilized in thetransient operating condition, as well as 176 and utilized in the steadystate condition, as such that the variable orifices must still have thearea thereof increase inversely proportional to the square root of thepressure drop thereacross. Under these conditions, the linearcharacteristic above referred to is maintained and the operationalcharacteristic of this system is obtained.

The linear relationship between the pressure drop across the floworifice with respect to the flow rate is illustrated in FIG. to whichreference is hereby made. As is illustrated in FIG. 5, pressure dropacross the orifice is plotted on the abscissa in pounds per square inchwhile flow rate in gallons per minute is plotted along the ordinate. Asillustrated under steady state flow conditions, a linear relationship ismaintained along the curve 190 while under transient flow conditions, agreater flow rate is required as illustrated along the curve 192 and alinear relationship is maintained.

Referring again to FIG. 2, the shutoff valve constructed in accordancewith the present embodiment of the invention is illustrated. As istherein shown, the housing 150 defines a second bore 202 within whichthere is positioned a slidable piston 204 which is sealed by an O-ring206 to the inner surface of the bore 202 as is well known in the art. Acap 208 is held in position over the opening to the bore in seatingrelationship therewith by bolts 210 as is well known. The inner portionof the capular weight provides a casteoltion 210 through which fluid maybe provided by way of the conduit 214 in response to movement of thespool 98 as described in conjunction with FIG. 1. A spring 216 abuts anadditional cap 218 which seals the opposite end of the bore 202 andwhich is held in place by the bolts 220 as illustrated. The spring 216is received within a bore 222 of the piston 204 and constantly purgesthe piston toward the cap 208. The two ends of the piston areinterconnected by a reduced diameter portion 224 which provides a pathfor the flow of fluid from the flow 156 through the flow area 226 andout the conduit 20 as illustrated.

In the event a differential pressure difference between the source andreturn flow paths in the system is detected of sufficient magnitude tocause a translation of the spool 98 as previously described, fluid underpressure is applied through the conduit 130 to the conduit 214 and intothe hollow area 228 of the piston 204. The fluid pressure operatingagainst the surface of the piston 204 causes it to translate upwardly asviewed in FIG. 2 against the force of the spring 216 in such a manner asto close the opening between the flow path 156 and the flow path 226thus shutting off flow of fluid from the source thereof to the conduit20 as previously described. So long as fluid pressure is maintainedwithin the hollow piston area at 228, the piston is retained in thepostiion so that flow is shut off. As soon as the pressure is relieved,the spring 216 returns to the piston 204 to the position shown in FIG. 2so that flow is once again established.

Referring again to FIG. 3, a check valve is illustrated generally at230. The check valve 230 includes a popit 232 which seats against a seat234 provided as a part of the bore 192 of the housing 190. A spring 236maintains the seat and popit in closed sealed relationship in the eventa break occurs in the conduit 24 and fluid is cut off from the source.In this manner, leakage from the return for the system is precluded. Thespring 236 is retained in place within the hollow inner portion of thepopit 232 and abuts a fitting 238 which is held in place by bolts suchas that shown at 240. Flow ports 242 are provided in the popit 234 sothat during normal return flow, the popit 232 is translated toward theleft and against the stop 244 provided by the fitting 238 therebypermitting fluid flow through the ports 242 and out the conduit 32 toreturn. I

What is claimed is:

1. Apparatus for detecting a flow difference. in first and second fluidflow paths and shutting off flow therein comprising:

A. first means in said first fluid flow path for producing a firstpressure drop which varies linearly proportional to changes in the flowof said fluid in said first fluid flow path;

B. second means in said second fluid flow path for producing a secondpressure drop which varies linearly proportional to changes in the flowof said fluid in said second fluid flow path;

C. comparing means for detecting a difference between said first andsecond pressure drops and providing an output signal upon apredetermined magnitude of such difference; and

D. means responsive to said output signal for blocking fluid flow in oneof said first and second fluid flow paths.

2. Apparatus as defined in claim 1 wherein said first and second meansare variable orifice means the area of which increases proportionally tothe square root of the pressure drop.

3. Apparatus as defined in claim 2 wherein said first and secondvariable orifice means includes first and second cylinders definingcontoured flow openings therethrough and piston means for selectivelyincreasing the area of said openings responsive to increased flowtherethrough.

4. Apparatus as defined in claim 1 wherein said comparing means includestransducer means and amplifier means.

5. Apparatus as defined in claim 4 wherein said transducer means is abellows comparator, s'aid amplifier is a double-nozzle flapper valve,and said flapper is positioned by differences in said first and secondpressure drops through the comparator.

6. Apparatus as defined in claim 1 wherein said comparing means includesfirst and second expansiblecontractable means connected to receive thepressure differentials across said first and second means for producingsaid first and second pressure drops respectively.

7. Apparatus as defined in claim 6 wherein said first and secondexpansible-contractable means is a first and second bellowsrespectively.

1. Apparatus for detecting a flow difference in first and second fluidflow paths and shutting off flow therein comprising: A. first means insaid first fluid flow path for producing a first pressure drop whichvaries linearly proportional to changes in the flow of said fluid insaid first fluid flow path; B. second means in said second fluid flowpath for producing a second pressure drop which varies linearlyproportional to changes in the flow of said fluid in said second fluidflow path; C. comparing means for detecting a difference between saidfirst and second pressure drops and providing an output signal upon apredetermined magnitude of such difference; and D. means responsive tosaid output signal for blocking fluid flow in one of said first andsecond fluid flow paths.
 2. Apparatus as defined in claim 1 wherein saidfirst and second means are variable orifice means the area of whichincreases proportionally to the square root of the pressure drop. 3.Apparatus as defined in claim 2 wherein said first and second variableorifice means includes first and second cylinders defining contouredflow openings therethrough and piston means for selectively increasingthe area of said openings responsive to increased flow therethrough. 4.Apparatus as defined in claim 1 wherein said comparing means includestransducer means and amplifier means.
 5. Apparatus as defined in claim 4wherein said transducer means is a bellows comparator, said amplifier isa double-nozzle flapper valve, and said flapper is positioned bydifferences in said first and second pressure drops through thecomparator.
 6. Apparatus as defined in claim 1 wherein said comparingmeans includes first and second expansible-contractable means connectedto receive the pressure differentials across said first and second meansfor producing said first and second pressure drops respectively. 7.Apparatus as defined in claim 6 wherein said first and secondexpansible-contractable means is a first and second bellowsrespectively.